1. Field of the Invention
The present invention relates to a magnetoresistive head comprising a magnetoresistive element for reading data signals which have been recorded on a magnetic recording medium.
2. Description of the Related Art
In the prior art, converters for magnetic readout, termed magnetoresistance (MR) sensors and magnetoresistive (MR) heads, have been disclosed, and it is known that such devices are capable of readout of data from magnetic surfaces at high linear densities. MR sensors detect magnetic field signals through changes in resistance as a function of the magnetic flux intensity and direction detected by a read element. These MR sensors of the prior art operate on the basis of the anistropic magnetoresistance (AMR) effect, whereby one component of the resistance of the MR element changes in a manner proportional to the square of the cosine of the angle between the magnetization direction and the direction of sense current flow through the element. A more detailed discussion of the AMR effect is provided in the monograph by D A Thompson et al., "Memory, Storage, and Related Applications" IEEE Trans. on Mag. MAG-11, p. 1039 (1975). In magnetic heads which operate on the AMR effect, it is common practice to apply a longitudinal bias in order to suppress Barkhausen noise. In some cases antiferromagnetic materials such as FeMn, NiMn, and nickel oxide are employed as materials for applying longitudinal bias.
A more notable magnetoresistance effect has been reported more recently. Specifically, changes in resistance in stacked magnetic sensors are caused by spin-dependent conduction electron transfer among the magnetic layers through the nonmagnetic layers and concomitant spin-dependent scattering at proximate layer interfaces. This magnetoresistance effect is known by several names, including the "giant magnetoresistance effect" and "spin valve effect". Such magnetoresistance sensors are constructed of suitable materials and offer improved sensitivity and greater changes in resistance than seen with sensors employing the AMR effect. In this type of MR sensor, the planar resistance between a pair of ferroelectric layers separated by a nonmagnetic layer changes proportionally to the cosine of the angle between the magnetization direction in the two layers.
Japanese Laid-Open Patent Application 2-61572 discloses a stacked magnetic structure in which large changes in MR are produced by developing antiparallel magnetization within the magnetic layers. The publication cites ferromagnetic transition metals and alloys as materials which can be used in the stacked structure. Also taught is a structure in which an antiferromagnetic layer is attached to one of the at least two ferromagnetic layers separated from the middle layer, and the use of FeMn for the antiferromagnetic layer.
Japanese Laid-Open Patent Application 4-358310 discloses an MR sensor comprising two ferroelectric thin film layers partitioned by a thin film layer of a nonmagnetic metal. The magnetization directions in the two ferroelectric thin film layers are perpendicular when the applied magnetic field is zero, and the resistance between the two unconnected ferroelectric thin film layers changes proportionally to the cosine of the angle between the magnetization direction in the two layers, independent of the direction of current flow through the sensor.
Japanese Laid-Open Patent Application 6-203340 discloses an MR sensor comprising two ferroelectric thin film layers separated by a thin film layer of a nonmagnetic metal material. The effect described above is achieved through the fact that when the externally applied magnetic field is zero, the magnetization in an adjacent antiferroelectric layer is maintained perpendicular to that in the other ferroelectric layers.
Japanese Laid-Open Patent Application 7-262529 discloses a magnetoresistive element which functions as a spin valve comprising a first magnetic layer/nonmagnetic layer/second magnetic layer/antiferroelectric layer structure, and particularly one in which the first and second magnetic layers consist of CoZrNb, CoZrMo, FeSiAl, FeSi, or NiFe, or of these materials with added Cr, Mn, Pt, Ni, Cu, Ag, Al, Ti, Fe, Co, or Zn.
Japanese Laid-Open Patent Application 7-320237 discloses a yoke type magnetoresistive element composed of an artificial lattice magnetoresistive film which comprises two or more stacks, each consisting of two or more types of magnetic thin films exhibiting different coercive force values and stacked with an intervening nonmagnetic layer, and a yoke provided thereto via a nonmagnetic insulating layer. The characterizing feature of this magnetoresistive element is that where HC2 and HC3 (0&lt;HC2 N HC3) represent the coercive force values of adjacent magnetic thin films, and where the y-axis is defined as the magnetization direction under zero magnetic field at saturation magnetization in the magnetic thin film which exhibits coercive force HC3 and the z-axis is defined as the direction running from the aforementioned magnetoresistive film towards the yoke and perpendicular to the film surface of the magnetoresistive film, the flow of current through the magnetoresistive film runs in the negative direction on the x-axis thus defined.
Oyo Jiki Gakkai Shi p. 113-116, Vol. 19, No. 2, (1995) describes an example of a flux guide type playback head which employs an anisotropic magnetoresistive element.
However, the shield type magnetoresistive heads which constitute the majority of types currently in use have problems in terms of potential corrosion and low durability due to exposure of the magnetoresistive element at the head air bearing surface (ABS). On the other hand, with a yoke type or flux guide type magnetoresistive head, which are designed such that the magnetoresistive element is recessed back from the ABS and an external magnetic field is induced to the magnetoresistive film via a soft magnetic yoke or flux guide, the symmetry of the reproduced waveform is greatly improved, the problem of corrosion of the magnetoresistive film is eliminated, and durability is excellent. However, yoke type or flux guide type magnetoresistive heads have the drawback that magnetic flux loss in the yoke or flux guide can result in significantly lower playback output than with shield type artificial lattice magnetoresistive elements.